: HAD may include damage to the nigrostriatocortical pathway, with resultant dopamine (DA) deficiency and impaired neurotransmission. This may present clinicallysd as Parkinsonism in HIV- 1-infected patients. Because of the complex regional and cellular heterogeneity in the brain, standard measures of efficacy for HAART therapy are irrelevant in predicting neuroloRic disease. In this Proiect we will identify the molecular and cellular correlates of HIV- 1-induced damage to vulnerable dopaminerRic pathways in order to select the most rational, tolerable, and efficacious therapeutic agents for clinical trials in Project 4. Our unifying hypothesis is that many symptoms of HAD, including Parkinsonism, are secondary to a reversible metabolic encephalopathy, which occurs in the setting of chronic inflammation from candidate HIV-1 neurotoxins released from MPs and possibly astrocytes. In experiments outlined below, we will test whether immune activation of MP by HIV-1 infection and CD40 ligation, or Tat treatment, induces reversible metabolic dysfunction in the nigrostriatal pathway. In particular, we hypothesize that HIV-l-infected MPs produce Tat that is soluble, secreted, and can enter dopaminergic neurons to downregulate the production of dopamine (DA). We will test this by measuring DA release and metabolites in dopaminergic nigral neurons exposed to Tat or conditioned media (CM) from +/-CD40-treated HIV-1-infected MPs. We also hypothesize that MP secretory products can interfere with striatal synaptic transmission modulated by dopaminergic neurons. We will test this by measuring synaptic transmission in an electrophysiologic bioassay of nigral-striatal-cortical organotypic co-cultures exposed to HIV-1-MP CM. We further hypothesize that at low doses of candidate HIV-1 neurotoxins these effects are reversible. However, after sustained exposure to low doses or high doses secondary to increased brain-resident MP burden and immune activation, the net result is permanent neuronal damage and death to neurons in this pathway. Finally, we will perform single cell aRNA profiling in neurons in the nigrostriatocortical pathway in order to identify critical molecular targets for neuroprotective strategies. We will focus on genes that regulate dopaminergic synthesis, degradation, and uptake, as well as release, in order to identify the most promising neuroprotective agents against candidate HIV-1 neurotoxins.